Seems a little outdated, phones and speeds have moved on a lot since, I know some countries have high speed 4G networks, but what is the reasonable page size for a website on a 3G network. I know this is a difficult question to answer as it has a lot to do with the user's expectations and patience, however I'm guessing that when developing a site you have a number that you aspire to.
There are many different mobile devices each with different screen resolutions. If you want to make sure it will look good on all mobile devices, it is highly recommended that you stick with 320 x 480 screen res*o*lu*tion and if possible, make it auto resize or auto center in order that it will not seem out place when viewed in mobile devices that has a bigger resolution.
You would not use fixed sizes when making your design. You'll use ems for your fonts and percentages for your layout. This is called fluid layout. I recommend you Google responsive design to learn about making your site work on desktops, tablets, and mobile units.